The present invention relates to a bearing system for a transversely installed engine-transmission (motor-transmission) unit in the body of a motor vehicle, having a first bearing element arranged between the engine and the vehicle body, and having a second bearing element arranged between the engine or the transmission and the vehicle body, and having a third bearing element arranged between the transmission and the vehicle body.
Such a bearing system is described, for example, in European Published Patent Application No. 0 818 340.
In the conventional bearing system for engine-transmission units installed transversely in a vehicle, the second bearing element provided at the bottom of the engine has assigned to it a movable hinged support, which transmits forces essentially in the rod direction of the hinged support. The disadvantage of the bearing system described in European Published Patent Application No. 0 818 340 is that it requires a technically complicated construction of the individual bearing elements, and is therefore costly. In addition, hinged supports tend to cause undesirable rod resonances and thereby contribute to an increase in the noise level of the vehicle. In addition, the accommodation of hinged supports often results in problems with respect to construction space and crash safety.
It is one object of the present invention to provide a bearing system for an engine transmission unit which minimizes the transmission of undesired vibrations to the vehicle body and which may be manufactured cost-effectively.
The above and other beneficial objects of the present invention are achieved by providing a bearing system in which the second bearing element is designed and arranged on the engine or transmission and the vehicle body, without a movable intermediate element, so that, through the second bearing element, supported torque forces of the engine transmission unit, are conducted, substantially in the longitudinal driving direction, to the vehicle body, and in which the second bearing element in a first domain, which encompasses small deflections in vehicle longitudinal direction about the static position of rest at standstill of the engine has a first spring rate, and in a second domain, which adjoins the first domain and encompasses larger deflections in the vehicle longitudinal direction, has a second spring rate, the second spring rate being greater than the first spring rate.
One advantage of the bearing system according to the present invention is, that because of the soft spring characteristic, during small deflections, idling vibrations may be isolated particularly well. Ideally, in this situation, the first spring rate may be almost zero, so that a loss effect results. By the second spring rate, greater in comparison to the first spring rate, load change impacts, in particular, can be effectively reduced. Therefore, the bearing system according to the present invention makes it possible to combine opposite and seemingly contradictory technical vibration requirements in one bearing system. The bearing system according to the present invention, which provides for conducting the torque forces of the engine-transmission unit substantially in or counter to the driving direction, achieves technical vibration advantages, which are based on the fact that vehicle bodies are relatively stiff in this direction, and thus are relatively insensitive to vibration. In addition, a limit stop may adjoin the region of the second spring rate.
According to a further aspect of the present invention, the second bearing element may be positioned below, i.e., vertically below, the first bearing element.
A particularly improved vibration isolation may be achieved by arranging the third bearing element in a position next to or on the torque-roll axis, and/or arranging the first bearing element in a position above the torque-roll axis. For this purpose, the torque-roll axis is defined as follows: If a very flexibly supported, rigid body is loaded with an vibrating torque parallel to one of its three main axes, this body will vibrate about this main axis. If the torque vector is not parallel to a main axis, this vector may be split into components parallel to the main axes. The individual components generate vibrations about the main axes, the vibrating amplitudes of which are functions of the primary mass moment of inertia and the components of the torque vector. The individual rotary vibrations are superimposed to one total vibration, the axis of rotation of which is generally parallel to neither the torque vector nor the main axes. The rotary vibration axis thus formed is referred to as the torque-roll axis.
According to one example embodiment of the present invention, a bearing system is provided in which the second bearing element includes a first anchoring part, and, relatively movable to this, a second anchoring part, at least one spring element acting between the first and the second anchoring part. The bearing element may be connected with the engine or the transmission and with the vehicle body, without movable elements such as hinged supports.
A particularly compact design is achieved when the second bearing element is a sleeve bearing, in which the second anchoring part encloses the first anchoring part at a radial clearance. Without substantial cost, this arrangement yields a stop function and crash safety.
Isolating the vibrations of the engine-transmission unit is improved further by the second bearing element having a first chamber filled with damping fluid and bounded by a first chamber wall, and a second chamber, separated from the first chamber by a second chamber wall connected to the first chamber via a passage, the volume of the first chamber being changed by a relative movement of the first and second anchoring part, so that damping fluid in the passage between the first and second chamber is moved.
According to a further aspect of the present invention, the first and/or the second chamber wall is formed as an elastic partition which, in the static position of rest at standstill of the engine, is arranged so that the volume of the first chamber is not changed during a relative movement of the first and second anchoring parts in the domain of small excursions about the static position of rest at standstill of the engine and so that, during a relative movement of the first and second anchoring parts in the domain of large excursions the volume of the first chamber is changed. In this manner, a release effect occurs with respect to damping in the second bearing element functioning as torque support, since hydraulic damping starts only when the excursions exceed a specific threshold value.
A construction that is particularly simple to produce as well as being compact is achieved by arranging the first and/or second chamber wall in the static position of rest at standstill of the engine at a clearance from the spring element. This clearance achieves that, at small excursions about the static position of rest, no changes in the volume of the first chamber, and, therefore, also no hydraulic damping are attained. If the excursions are larger and exceed the aforementioned clearance, changes in the volume of the first chamber, and consequently the desired damping, begin to occur.
Thus, spring rates, which are of different magnitudes in the domain of small and large excursions, may be achieved particularly advantageously in that, in the first and/or second chamber in particular, elastic bumpers are provided, which stop the relative movement between the first and second anchoring parts. In the domain of large excursions, the spring rates of the elastic bumpers are additive to the spring rates of the spring element. Very low dynamic stiffnesses may also be achieved by bridging the gap using rubber crosspieces and by providing large passages in the region of the outer connection of the spring element to the second anchoring part. Thus, a hydraulic quenching function may be achieved during idling, in which the support acts softer than in the static state.
A particularly improved isolation of vibrations may be achieved when a first, second and/or third bearing element is positioned at body locations having high stiffness, particularly in the region of the chassis attachment. These bearing elements may be fastened to the vehicle chassis or to a subframe of the body. All bearing elements may be connected to the engine-transmission unit and the vehicle body without movable intermediate elements.
In accordance with one cost-effectively manufactured example embodiment of the present invention, the engine-transmission unit is fastened to the vehicle body by exactly three bearing elements. The first, second and third bearing elements, according to the present invention, are sufficient in most cases for achieving a sufficient bearing system of the transversely installed engine-transmission unit, from a technical vibration aspect. In addiction to the three bearing elements, arranged and designed according to the present invention, one or more further bearing elements may be provided.
Furthermore, the first bearing element may be positioned at or adjacent to the upper end of the engine-transmission unit, and the second bearing element may be positioned at or adjacent to the lower end of the engine-transmission unit. In accordance with a clearance of these bearing elements, an improved vibration isolation may be achieved.
The first and the third bearing elements may be positioned so that the center of gravity of the engine-transmission unit is arranged below an imaginary connecting line between the first and the third bearing elements.